Electric motors conventionally comprise a housing, a stator in the housing and a rotor rotatably mounted in the housing and adapted to be rotated when the electrical power is supplied to the stator. The stator may comprise a plurality of laminations which, in turn, support a plurality of windings. Such a motor further includes a strain relief device which isolates the external leads from the wiring of the stator.
In an electric motor such as shaded pole motor, for example, the stator may have two or more integral segments extending radially inwardly and a coil may be wound about each of the segments. In the manufacture of stators, it is common to apply an insulator coating such as an epoxy coating to the stator before the coil is wound about the segment of the stator to isolate the windings of the coil from the metal of the stator.
In such electric motors, it is common to provide a protector between at least one pair of coils, such as bi-metallic devices, to open and close the winding at a pre-set calibration temperature and thereby prevent the electric motor from overheating in a locked condition. Electric motors having 45 watts or more input require cooling from the operating load or from an internal fan to protect the motor from overheating during the running cycle. If for any reason the motor is unable to run, either from bearing failure or from lock-up of load, the cooling system becomes inoperative and the current in the motor increases from 150 to 300 percent of the rated input power.
Where the electric motor is installed in a secluded location and the motor has an automatic thermostatic device which does not alert anyone that the motor is locked -up and is cycling on the overload mode, the overload device will fail in a closed circuit mode allowing the locked rotor to increase and accelerate the increase in temperature.
In accordance with the invention, a unitary motor overload assembly is provided and connected by a standard insulated lead from one of the coils and by a solid uninsulated conductor lead to the other of the coils, the cross-section of the solid conductor being such that the motor will operate satisfactorily during normal running or locked rotor condition but would open by melting in the event of a winding failure of the coils which would normally result in higher than normal operating currents in the winding.
The invention has particular utility in connection with the electric motor shown in the patent application filed concurrently herewith entitled "ELECTRIC MOTOR", Case R-675, Ser. No. 07/470,618, filed Jan. 26, 1990, having a common assignee with the present application, wherein the electric motor comprises a stator having a plurality of radially inwardly extending circumferentially spaced polar segments and a plastic stator member on each axial end of the stator. Each member has substantially the same configuration as the cross sectional configuration of the ends of the stator, including segment portions overlying the segments of the stator. Each segment portion includes an axially outwardly extending wall and a coil is wound around each stator segment and segment portion of said stator member. Integral strain relief portions are provided on each stator member for connecting the coils and for connecting power leads to the ends.